ALSA: hda: hdac_ext_stream: fix potential locking issues

The code for hdac_ext_stream seems inherited from hdac_stream, and
similar locking issues are present: the use of the bus->reg_lock
spinlock is inconsistent, with only writes to specific fields being
protected.

Apply similar fix as in hdac_stream by protecting all accesses to
'link_locked' and 'decoupled' fields, with a new helper
snd_hdac_ext_stream_decouple_locked() added to simplify code
changes.

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20210924192417.169243-4-pierre-louis.bossart@linux.intel.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>

include/sound/hdaudio_ext.h

@@ -88,6 +88,8 @@ struct hdac_ext_stream *snd_hdac_ext_stream_assign(struct hdac_bus *bus,
 					   struct snd_pcm_substream *substream,
 					   int type);
 void snd_hdac_ext_stream_release(struct hdac_ext_stream *azx_dev, int type);
+void snd_hdac_ext_stream_decouple_locked(struct hdac_bus *bus,
+				  struct hdac_ext_stream *azx_dev, bool decouple);
 void snd_hdac_ext_stream_decouple(struct hdac_bus *bus,
 				struct hdac_ext_stream *azx_dev, bool decouple);
 void snd_hdac_ext_stop_streams(struct hdac_bus *bus);

sound/hda/ext/hdac_ext_stream.c

@@ -106,6 +106,25 @@ void snd_hdac_stream_free_all(struct hdac_bus *bus)
 }
 EXPORT_SYMBOL_GPL(snd_hdac_stream_free_all);
 
+void snd_hdac_ext_stream_decouple_locked(struct hdac_bus *bus,
+					 struct hdac_ext_stream *stream,
+					 bool decouple)
+{
+	struct hdac_stream *hstream = &stream->hstream;
+	u32 val;
+	int mask = AZX_PPCTL_PROCEN(hstream->index);
+
+	val = readw(bus->ppcap + AZX_REG_PP_PPCTL) & mask;
+
+	if (decouple && !val)
+		snd_hdac_updatel(bus->ppcap, AZX_REG_PP_PPCTL, mask, mask);
+	else if (!decouple && val)
+		snd_hdac_updatel(bus->ppcap, AZX_REG_PP_PPCTL, mask, 0);
+
+	stream->decoupled = decouple;
+}
+EXPORT_SYMBOL_GPL(snd_hdac_ext_stream_decouple_locked);
+
 /**
  * snd_hdac_ext_stream_decouple - decouple the hdac stream
  * @bus: HD-audio core bus
@@ -115,19 +134,8 @@ EXPORT_SYMBOL_GPL(snd_hdac_stream_free_all);
 void snd_hdac_ext_stream_decouple(struct hdac_bus *bus,
 				  struct hdac_ext_stream *stream, bool decouple)
 {
-	struct hdac_stream *hstream = &stream->hstream;
-	u32 val;
-	int mask = AZX_PPCTL_PROCEN(hstream->index);
-
 	spin_lock_irq(&bus->reg_lock);
-	val = readw(bus->ppcap + AZX_REG_PP_PPCTL) & mask;
+	snd_hdac_ext_stream_decouple_locked(bus, stream, decouple);
-
-	if (decouple && !val)
-		snd_hdac_updatel(bus->ppcap, AZX_REG_PP_PPCTL, mask, mask);
-	else if (!decouple && val)
-		snd_hdac_updatel(bus->ppcap, AZX_REG_PP_PPCTL, mask, 0);
-
-	stream->decoupled = decouple;
 	spin_unlock_irq(&bus->reg_lock);
 }
 EXPORT_SYMBOL_GPL(snd_hdac_ext_stream_decouple);
@@ -252,6 +260,7 @@ hdac_ext_link_stream_assign(struct hdac_bus *bus,
 		return NULL;
 	}
 
+	spin_lock_irq(&bus->reg_lock);
 	list_for_each_entry(stream, &bus->stream_list, list) {
 		struct hdac_ext_stream *hstream = container_of(stream,
 						struct hdac_ext_stream,
@@ -266,17 +275,16 @@ hdac_ext_link_stream_assign(struct hdac_bus *bus,
 		}
 
 		if (!hstream->link_locked) {
-			snd_hdac_ext_stream_decouple(bus, hstream, true);
+			snd_hdac_ext_stream_decouple_locked(bus, hstream, true);
 			res = hstream;
 			break;
 		}
 	}
 	if (res) {
-		spin_lock_irq(&bus->reg_lock);
 		res->link_locked = 1;
 		res->link_substream = substream;
-		spin_unlock_irq(&bus->reg_lock);
 	}
+	spin_unlock_irq(&bus->reg_lock);
 	return res;
 }
 
@@ -292,6 +300,7 @@ hdac_ext_host_stream_assign(struct hdac_bus *bus,
 		return NULL;
 	}
 
+	spin_lock_irq(&bus->reg_lock);
 	list_for_each_entry(stream, &bus->stream_list, list) {
 		struct hdac_ext_stream *hstream = container_of(stream,
 						struct hdac_ext_stream,
@@ -301,18 +310,17 @@ hdac_ext_host_stream_assign(struct hdac_bus *bus,
 
 		if (!stream->opened) {
 			if (!hstream->decoupled)
-				snd_hdac_ext_stream_decouple(bus, hstream, true);
+				snd_hdac_ext_stream_decouple_locked(bus, hstream, true);
 			res = hstream;
 			break;
 		}
 	}
 	if (res) {
-		spin_lock_irq(&bus->reg_lock);
 		res->hstream.opened = 1;
 		res->hstream.running = 0;
 		res->hstream.substream = substream;
-		spin_unlock_irq(&bus->reg_lock);
 	}
+	spin_unlock_irq(&bus->reg_lock);
 
 	return res;
 }
@@ -378,15 +386,17 @@ void snd_hdac_ext_stream_release(struct hdac_ext_stream *stream, int type)
 		break;
 
 	case HDAC_EXT_STREAM_TYPE_HOST:
+		spin_lock_irq(&bus->reg_lock);
 		if (stream->decoupled && !stream->link_locked)
-			snd_hdac_ext_stream_decouple(bus, stream, false);
+			snd_hdac_ext_stream_decouple_locked(bus, stream, false);
+		spin_unlock_irq(&bus->reg_lock);
 		snd_hdac_stream_release(&stream->hstream);
 		break;
 
 	case HDAC_EXT_STREAM_TYPE_LINK:
-		if (stream->decoupled && !stream->hstream.opened)
-			snd_hdac_ext_stream_decouple(bus, stream, false);
 		spin_lock_irq(&bus->reg_lock);
+		if (stream->decoupled && !stream->hstream.opened)
+			snd_hdac_ext_stream_decouple_locked(bus, stream, false);
 		stream->link_locked = 0;
 		stream->link_substream = NULL;
 		spin_unlock_irq(&bus->reg_lock);